Set of fused bifocal-lens blanks



Wave 3, jggg.

e. A. CLEMENT SET OF FUSE!) BIF'OGAL LENS BLANKS 2 Sheets-Sheet 1 Filed July 1. 1924 INVENTOR,

- ATTORNEYS.

- Pakeniefi New". 3, 1%25.

GEORGE A CLEMENT, OF MGUN'Z. VEBNQN.

fil iffifllii'll. TING A COKPORATION NEW TIGER, ASSIGNOR TU PATEIIE (JPTICAL GL EELAW'ARE.

SET 01 FUSELD BIFOCAL-LENS BLANKS.

ekgiplieation filed July 1,

UWILJ EURfll-E A. CLEMENT, Stems residing at (154' whom 'ilI(Z- l/ un it known film? (1 citizen 0% the Unileii i ioimt Vernmn in the ceunty of l/Vestehester 'mil si'zuie efllvw York, have invented cerin new and useful lmpri'ivemenls in Sets Jill Fused Bifocal-Lens Blanks, of which the following is 21 full, clear, and exact lescriptien.

lily invention. rel if making fused; blanks "formed by glass knewn as 19 ales generally to the art liming a small piece at liutl'on 1n segment, in a 'col'mtei'sink Oi depression in one {face 0 a large! 01' major [)lii'fi (if lass, lhe Sll'lilll piece of heing of a higher imlex of. re fraction than that of the major piece 0f glnss. f mni'nenly, the button is mmpesml of ili'nt glass and ilie n jorlws portion is ((impuseil of crown glass.

meniseus mtm'ie shape, the countersink IS in the enter 0:,- cenvex face and in finishing the hhmk to the desired ienticiihufor 1, tnis outer or hil'ocal side of "(he blank given a wnfinueus splierienl unwal'm e, while the 0pposirs; fare is finisheil to i'lji: requisite spherimil or e -,linih-ie;xl form to satisfy the -.u'tieiilm. pi'esmsintiun. Although the bifocal side habil minimums curvature thefecal waiver through the segi'n'ent pin-film ill the lens is greater than that of the major pei'iien due .0 the higher index n? refraction of the flint glass. The area (if the lens occupied by the segment 01' flint glass surface lhei'e'i'ore CQlllprisus ihe nemr Y i en or reading field, \Yll'ilQ. the major pmtinn of the lens composed Wholly of crown glass the: ('lisinnce vision field, and fl hehveen the two iieliis is (li 'zien.

' This i'l'lldfili power l-znewn as the adl'hi'migzh the reading field is determined both by the index of refraction of the flint glass mil also by the curvatures of its faces" Since the, finished. 'eui'vature of the outer face of the flint glass is (he same as that of the major lens portion and since ilnas been the stamlm-clpmetice l1; finish (his outer snr'fm-e to one of large niiz'nl'ier nf different (ill'i iltillfifi in producing viii'ioizs' Emile-alarpewers 01" the dis fiance field, ii lms been necessary Wide range ef'eur'va flint inittens wiih lures in their inner faces an emle r t0 0hhl'foeal lens blanks, ilmt is,

ln blanks hf 1e il'iileiienec in fecal pewer I in make the i 1924. Serial N9 7255, 161.

teiin ihe desired addition for all bifocal prescriptions.

in accordance with my patenieil in {he United States in Letters Pnl'ent ifzl lil-lqilkli at? May 20, 1924, I propesed to ohmin the various desired additions for a cmnylele set of blanks by employ ing sei'elal (liii'erent flint glasses of different inilives of veil-action, which enabled me to llllllfllillll the inner face of the button con-- stunt Eur all ihe blanks (lithe set, thereby not only nmierinily reducing the number of hizmlis, which the dispenser mnst keep in slm'li. hui also substantially reducing the mmmleciming vest. According to the (liselesures ei? that pnlent the surface of the depression n'ml liPDCk ll I the flint hullen was preferably made plane; although ii was explained that other gem metrii-nl fin-ms might he employed tler this wir'l rmx I The cimi'n glass hlanlis in which the mimiei'sinl; is farmed are, as a rule, dropped or mehletl, :2, hur-nem'ly all heingg of meniscus shape. The ltlllll' have iieen .niohleil to a variety of viii-Yes, known as the base curves, the most umnnmn practise being to employ the S-bas curve s vsmn n:in1ely, 3 alioptei's, 6 dioptel's 21ml. 9 iliu n'ms. The-various base curves result in providing blanks which approximate \he eiii'vai'm'e which a lens grinder is called ini'in'm on he faces of the blank in filling prusvript'ieiis, and therefore, by properly uelvvl me; his blanks the grinder 1.; enabled to n'i'mimimhe nmnswsmy grinding Operation, lillflR hem. lhe practiw, however,.to depart 'li'mn thew huse curves in finishing both the miter and inner faces of the lens "from the blank. The vm'vmxmwe ofxthe outer face, i'mvmmiple, must he such as t0 effect the flesh-ell :nhiitiun; while that 1: the inner face. must he suirh as to satisfy the prescription wilh respect in'the lenticnlm' power of t distance iiehl. For instance, a lols.

nmhled to n 9 diepter husecurve might have its outer face finished to a $150 '(liepters to ehtain the addition mllecl for by the pre seriptien, While mammlsice might be. finisliecl to :1. (liopteii curve. TlllSflE'OlllCl he. the easse,'fnr exnn'iple, with a, blank having a flint gln io a ma ler grown glass lens of. index 31.53

Owner invention r-nmill percentage being piano,

1e inner surface of? button e'E inclex 1.62 fused when the curvature of the countersink is -1.50 diopters and the. prescription called for a correction of +2.50 diopters' for dis tance and an addition of 2 diopters.

This necessity of finishingthe outer face of the blank to a curvature different from the base curve was also characteristic of embodiments of my said former invention. In that case the outer finished curvature of the lens must be such as to give the desired ad dition with the particular index of refrac tion of the flint glass incorporated in the blank, and it is, therefore, necessary with such a set of blanks for the lens grinder to know the requisite curve for-the bifocal face of the lens for each prescription, and

grind the blank accordingly, the curvature of the minus or rear face being determined by the power of the distance field called for by the prescription.

In the practice which has heretofore commonly prevailed in the manufacture and distribution of fused bifocal blanks, as above explained, as well as in,the set of blanks contemplated by my said former invention, the blanks are of necessity sold in their grough or entirely unfinished condition. since ,the lens grinder is called upon to impart various curvatures to the bifocal side of the blank. My present invention is well adaptable to the practice of reducing the blanks to semi-finished form at the factory, that is, grinding and finishing the bifocal side of the lens, thereby requiring the lensgrinder to grind and finish only the inner face of the blanks to fill his prescriptions. It will be understood that this is preferable for several reasons, principally because more general uniformity of the finished roduct is thereby assured, and also because it e work which the dispenser is called upon to perform u on the blank is very substantially reduce less noticeable prismatic deviation through.

' It is a fact well .known to optometrists that certain relatively objectionable features of bifocal lenses are augmented with an in,- crease in the added power. Besides more or the reading portion of the higher additions, there are frequently observable more or less chromatic aberration and internal reflection of the rays of lightresulting, in effect, in a self-luminous medium through which the wearer looks and a constant diminution in his visual acuity. I have found that in the case of fused bifocal lenses this is due to a considerable extent, at least, to the fact that standard. practice the increase in the power of addition is largely obtained by an.

increase in the convexity of the inner face of the flint-"lass button. In other words-the countersink of the lenses of higher addition is a rclativeiy deep concavityand the segment becomes a wide angle prism which is so related to the eye of the wearer that the ea ers visual axis is quite oblique to the inner face of the button. Consequently not only is there greater prismatic deviation. but the chromatic aberration is intensified and the rays of light which coincide with the visual axis are at a decided angle to the radius of curvature of the inner face of the button and hence are reflected back and forth between the two surfaces of the button and, have the effect of internally illuminating the fiint glass.

By my invention I am able to'minimize these undesirable effects by properly shaping the button and relating it to the visual axis. My invention, briefly stated, resides in so relating the index of refraction of'the button and the outer curvature of the lens I This curve increases in power from series;

to series and is sufliciently great for, every series so that the lens blank of highest ad dition in every series has a countersink, the

surface of which is a plus curve. I have found that the absence of minus countersinks greatly lmproves the lenses in the respects referred to above. The periscopic shape of the button makes it possible to dispose it more nearly concentric with the eyeball, and it will be] appreciated that true concentricity is more nearly realized with each higher series since the radius of the outer finished curve becomes shorter from series to series toward the higher additions, thereby approaching coincidence of the visual axis with the radius of curvature of the inner face of the button toward the high additions where the objectional features are most pronounced in fused bifocal lenses as heretofore made. A further advantage of my invention is the fact that the lenses may be made thinner than is possible with blanks in which the button is bi-convex.

Another feature which is rendered possible by my invention and which my invention contemplates, is the employment of what is 'known as a wide angle se ment.

Heretoflore, in fused bifocal blanks m: dqiaccording; to the standard practice. the diameter of the segment has been limited 'because of the fact that the thickness of the segment has been. proportional to the size, since practically al the segments have plus curvatures for their inner faces.

fore, it the segment were larger than 25 mm. in diameter, the finished lenses would be too thick and consequently too heavy, at least for'the higher additions, since manifestly the inner side of the blank could not be ground down so as to wear away any or the inner face of the segment. Thostandard crown blank is substantially 50 mm.

Then

in diameter, and the diameter of the se mcnt oi fused bifocal lenses has, theretorc, beeu limited to substantially one-half the diameter ot tbc crown blank, part of the segment and o l the crown glsss being, of course, finally. removed in cutting out the lens. Since with my invention the flint glass scgmei'its are all concavo onvex in form, the thickness of the sc ment does not vary greatly, with the addition and I am, therefore, able to use scgments substantially greater than ouedml'f the diameter at the crown blank.

I shall. now more particularly explain my invention in connection with the appended drawings and sliall thereafter point out'my invention ,in claims: t

l is a face View oil a rough molded crowrrbleulz; I

52 shows in. section four such blanks molded to, respectively, 6, diopter curves;

Figs. 3 and 4t uroviews of Figs, 1 and 2, siter tlie been formed in. the blank;

Fig", 5 cud S are, respectively, a face View section or" a fiint button ready to :1 into the countersink; J

Fig. i" is a, sectional View of the rough blank utter the fusing oyerstiomf (l-is a, section of the black in semisimilar to those countersink finished form, that is, after the bi'iocul surface is finished;

Fig. a. table giving additions the curvature of the countersinlcs and the finished curves on the bifocsl'side of one set of blanks embodying my invention; I i

Fig. 1G. is bodimeut of my invention;

Eli lit similar table showing how my 1 {rt a set of invention may be cmbodic l blanks including not, only those of l 1g, 9

but Pi-Qffll alternative numbers for most of the additions,

The crown gloss blank 1 is formed byheutlug c sufficient quantity of glass to "plastic ccutlit'ozi and then molding it to the dc sired curvature. uuillustrstioml shall explain my invent-ion embodied in a set in which the finished curve on the bifocal side, for the screral serics is, respectively, (3 dioptcrs, 8 diopters, 1O diopters and 12 diopters, in order to facilitate the forma tion of these curvatures on the blanks of the respective series, the blanks 1 will be ggpldcd, some to the 6 diopteicurvature of the b'lsnlr 1* of Fig. 2, some to tho 8 di. opter curvutm'e of blank 1' of Fig. 2, some to the 10 dioptor curvature of blank 1 of Fig. 2, and some to i'bc i2 dioptcr curvature of lank of Fig. Tlberestter, there round from near tltc c .iter to one edge on the convex; ihcc of the blank u couutcrsmk 2, the cur mtur oi which will of my invention that e, 1e and 12 illustrated and will for the respective a similar table for another elmopter'series.

depend upon. which particular blank of the series is to be made,

that is, upon the addition, as will be later explained in QODIIQC- tion with Figs. 9, 10 and 11. A

segment 3 glass is then formed 01 a diameter segment 3 may be mm.

The segment 3 is then fused in the countersink once with the well known practice,

2 in accordas shown in Fig. 7 and thereafter the outer face 1s ground down and finished, 2i 6. As above explained, 1t 15 isbed either to a, 6,

this outer s shown in Fi a characteristic fact: is fluor 12 die tor curve in the illustrated instance, accor ing to the. series to which the blank belongs, and

that there is no departure two curvatures.

from these selec- I have shown in Fig fl' one way in which for my set may be made up ingjrom .25 diopters to additions rangdiopters, within which range ome practically all of the prescrlptlons that, a dispensing optlcmnis called upon to fill.

as well as-l or all the sets This from glass for this set,

which I have hereinafter describe, has

an index of refraction of 1.6973, and this fimt glass,

when fused to crown glass having so index of refraction of 1.53 will add 1- diopter 111 power when' its plane-convex curvature is idioptexs lit willbe secn th at tbeset illustrated in Fig. 9 1s divided into four series having their bifocal side finished, plus curves of '6 diopters,

' diopters and 12' dioptcrs.

The first five uuitsof the prised in the ,6 diopter serie. first unit. has an addition of oi a diopter, the focal power button must be ,4 that of button lisvin a curvature respectively, to 8 ,diopters, 10

series are com- Since the 25, th i /4 .of the flint lano convex 6 diopters,

since such a p 2110 convex button would add 2 dio'pters. That isobtai'ned by making the inner face of the opter curve. The the front and rear +175 diopters, and hence will add ,4; of a will be seen that the power the succeeding units of the difierenc is increased successively of a substructing .7 5

the countersink, that curve on the inner face flint button it. -52?) diethen betweenfaces in diopti c owcr is which is of 3 iogtcrs dioptr'l l o it of addition for 6 die )ter'scries 'iop ter by diopters from the curve; of 15, from the m nus of the button, making a plus curve of diopters for the countersink of the 1.25 addition unit, which is the highest series no this pturt culur sot. units of the set are comprised 1.5 0 button must he +4.50, wbicl addition the 6 diopter The next three within the 8 di- In order to give an addition of ,tcrs the effective curvature of the i is obtained by making a +3.50 curvature to the countersink.- and similarly it will be seen that countersinks of +2.75 and +2.00 diopter curves will give additions of 1.75 and 2.00 diopters with the finished curve of 8 bifocal side of the blank. I The next two numbers in this particular set are included in the 10 diopter series, and it will be seen that a +3.25 curvature of the countersink will give an effective curvature of +6.75 diopters to the button which will result in an addition'of 2.25 diopters. Similarly, it will be seen that a plus curvature of 2.50 diopters forthe countersink will give an efiective curvature of +7.50 for the button,. or an addition of 2.50 diopters.

The last five units of the set are comprised within the 12 dionter series and by computation it will readily be seen that the fiountersink curvatures indicated in the table bf Fig. 9'for the 12 diopter series will give the respective additions there indicated.

It is apparent that other valuesinight be selected for the finished curves of the bifocal side of the blanks of the several series and that the several series might be otherwise apportioned throughout the range of successive additions in such a manner as to have all of the countersinks of plus curvatures. Another plan is illustrated, for example, in Fig. 10 in which I have shown how the set might be made up of 5 series having for their bifocal side finished curves of, respectively,4, 6, 8, 10 and 12 dioipters. It will readily be seen that the first unit vhas an e'fi'ective curvature of +15 for the button and hence an addition of .25 diopters. In a similar manner it will be seen that each countersink curvature indicated in the second, horizontal row of Fig. 10 will. with the indicated finished curves (in the bifocal side, give the respective additions indicated in the first horizontal row of that figure.

In Fig. 11, I have consolidated in one table various alternative blanks for the sev-- eral additions, all of which have plus eonns tersinks. This illustrated set comprises only the 6, 8, 10 and 12 dio'pter series for the finished curves of the bifocal sides.- but it is manifest that a 4 diopter series could be added thereto, or that other curvatures might be employed for the several series. In the set illustrated in this table there are a plurality of units for all of the additions up to 3.25 diopters. there being four each for the first seven. additions three each for the next three additions. two each for the next three additions, and one for each of the last two additions. The advantagein such a multiple set is the fact that it gives the lens grinder greater latitude with respect to his tool equipment. \Vhile, for exznnplo, he might be unable with his tools to fill a prescription from one of the units for a certain addition, he would be able to do so from diopters on the some other unit having that addition. in the horizontal row of this table of 11 is given the respective additions, as in Figs. 9 and 10; and in the succeeding hori zontal rows are givenfirst the finished. curve of the bifocal side of the blank and there after the curves of the corinterimnits which will give the respective additions appearing v at the top of the columns, fit wiil. be Footerthat all of the countersini-is of this table are plus curves. f desired, a flint glass having a higher index of refraction might be used for the ni'inzhers which would he pieced-in the blank spaces so as to give plus eountersinks aecordiifig to my invention.

it is obvious that my invention is, not lii'nit-ed to the finished curvatures for the bi.- i ocal face of the blanks which have selected for illustration, nor to the psrticuiar index of refraction for the iiint gisiss which I here given in my explanation above and that various other respects in which the numbers may he changed from that illustrated in the tables of Figs. 9,1!) and 11, will readily oeprising a set of bifocal lens blanks 'irogress,

in o: from lowest to highest addition and each formed by fusing a small piece oi. glass having a relatively high index. of refraction into a plus countersink. in. the pin a major piece of glass of lower inuz of 1H. fraction, the set being; made up of s plural ity of series classified accordingto the finished curve on the bifocal side the curve being the same hir all the blanks each series but different for the series, and each series using made up ciapin" rality of units of progressively higher ad. ditione.

2. A product in the insnuiaeture of hir d cal lenses that have their entire bifocal sides finished entirely to continuous curves, cont prising a set of bifocal lens blanks progressing from lowest to highest a-dditii'm and each formed by fusing a small piece of glues having a relatively high index cit retraction into toplus countersink in the plus side of a major piece 0t glass of lower index at refraction, the set heing made up of ii plural" ity of series classified according to the finished curve on the bifocal siderthc curve being the same for ali the blanks of each series but different for the several series, and each series being made up of a plurality of units of progressively higher additions, characterized by the fact that the small pieces of glass throughout the of the some index of refraction and thesa index audthe curvature of the bifocal It "will he understood. that.

dill

Hit

ofthe units of each series are so related that the surface of the coul'itersink'of the unit of highest addition of each series is a plus curve. a

3. A product in the manufacture of bifocal lenses that have their entire bifocal sides finished entirely to continuous curves, e0n1- n-ising a set of bifocal lens blanks progressing from lowest to highest addition and each formed by fusing a sinall. piece of glass having a relatively high index of refraction into a plus.countersink in the plus side of a major piece of glass of lower index of refraction, the set being made up of a plurality of series classified according to the finished curve on the bifocal side, the curve being the same for all the blanksof each serieshut different for-the several series,

and each series being made up ofa plurality of unitsv of 'n'ogrcssiyely higher additions, cluu'acterizcd hy the fact that the diameter of the small piec of glass is substantially I greater than one ialf that of the major pieces and the index of refraction ofthe small pieces of glass and the curvatures of the bifocal side. 0% theumts of the several enonei i Al CLEMENT; 

